What am I thinking? Sorcerers can't quicken spells anyway, because all metamagic takes a full round action for them (including quicken).

Project image seems to say that you can cast spells from the image instead of yourself any time you want, from any school, but still only once per turn regardless of the kind of spell. You don't get an extra spell each turn no matter what. The difference with illusion spells is that when you cast from the image's POV the image can target itself (with other kinds of spells it can't). It could also target others with the illusions. I suppose you could use it to get better targetting angles or cast safely from around a corner (but still in view of the image), but otherwise I don't see much use for it. Perhaps not the best thing to dedicate a known spell to, unless you've thought of a way to use it all the time. But with its short duration, you'll probably only want to use it when you have a prep round (or else you'd blow a combat round on something questionably useful), which is a major downside.